1. Field of the Invention
This invention pertains to a novel method of drying pipelines which utilizes gelled pigs in combination with a dessicating alkanol in both gelled and liquid form.
2. Description of the Prior Art
Pipeline efficiency and volume can be lost by scale build-up in the interior linings of the pipe. In many instances, this scale also contains bacteria which attack the commodity to be transmitted by the pipeline. For example, sulfate-reducing bacteria can generate copious quantities of hydrogen sulfide on certain crude oils. Hydrogen sulfide is a noxious, toxic gas which makes the material difficult or dangerous to handle from a personnel standpoint and also from a pumping standpoint. Undissolved gases in a liquid can cause pumps to cavitate, lose prime, or to function less efficiently overall. Still other bacteria are known to consume hydrocarbons and result in a loss of product and cause some of the processing difficulties mentioned above.
Mechanical pigs and/or gelled chemical pigs have been used to remove the scale. The mechanical pigs are normally solid bullet-shaped devices which have wire brushes or abrasive surfaces to physically abrade the scale interior from the pipe. The gelled chemical pigs, on the other hand, remove the surface deposits by dissolution and/or by picking up loose debris as they pass through the pipeline.
A new aqueous gelled pig containing bactericides was described in a commonly owned co-pending patent application filed by Robert J. Purinton, Jr. on Nov. 20, 1979, entitled "Gelled Pigs for Cleaning and Sanitizing Pipelines", Ser. No. 096,106, the disclosure of which is incorporated herein by reference. The gelled pigs described there are extremely effective in removing bacteria-containing scale from pipelines.
Still other aqueous cross-linked gelled pigs for cleaning pipelines were described by Robert J. Purinton, Jr. in a U.S. patent application entitled "Aqueous Cross-linked Gelled Pigs for Cleaning Pipelines" filed December, 1979 (Attorney Docket No. C-27,974), the disclosure of which is incorporated herein by reference.
The pigs described in each of these applications by Purinton are effective in cleaning pipelines, but as noted by Z. A. Popan, Pipeline Gas Journal, Volume 204, No. 14, 20 (December, 1977), because water is an undesirable foreign matter in any oil or gas pipeline, the cleaning of pipelines should be associated with their drying. One method of drying the pipeline was described by G. D. H. Crawford, Gas Journal, Volume 341, No. 5549, 282 Mar. 18, 1970). Crawford removed the bulk of the water from the pipeline by conventional pigging using mechanical pigs and then swabbed the interior of the pipeline by passing a quantity of methanol through the pipeline sandwhiched between pigs. Crawford found it necessary to use this technique to remove residual water from pipelines carrying natural gas having a high proportion of methane. Residual water was said to form hydrates with the methane under certain conditions of temperature and pressure and lead to serious transmission difficulties.